1. Field of the Invention
The present invention is related to a radiation imaging apparatus. More specifically, the present invention is related to a radiation imaging apparatus that moves a device to be employed in radiation images, by an operator manipulating an operating handle provided on the device.
2. Description of the Related Art
Conventionally, it is uncommon for small scale medical facilities, such as physicians in private practice and clinics, to install radiation imaging apparatuses dedicated to imaging specific portions of subjects. These medical facilities generally employ a single radiation imaging apparatus to perform radiation imaging of various body parts as necessary. For example, radiation imaging systems, in which an upright imaging table and a supine imaging table are installed in a single imaging room, a radiation source is supported by a ceiling runner suspension device or the like, and the irradiation direction of radiation is adjusted to be toward the upright imaging table and the supine imaging table by moving or changing the orientation of the radiation source, are known (refer to Japanese Unexamined Patent Publication No. 2007-244569 and U.S. Pat. No. 7,641,391).
The ceiling runner suspension device of such a known radiation imaging system is equipped with: a ceiling horizontal movement base that moves along the ceiling in the horizontal direction; and a telescoping support column, which is mounted on the underside of the ceiling horizontal movement base and is capable of extending and contracting in the vertical direction by telescopic motion. There are known radiation imaging systems in which a radiation source is mounted to the lower end of the telescoping support column.
There is also a known radiation imaging apparatus of the type described above, in which a operating handle is provided on a radiation source, external forces which are applied to the operating handle are detected, and the radiation source is moved by drive means, such as motors, according to the external forces to assist manual movement (to provide “power assistance”) when moving the device (refer to Japanese Unexamined Patent Publication No. 2000-316838).
There are also known radiation imaging apparatuses having the power assistance function, in which a device is moved in the directions in which the external forces are applied at speeds corresponding to the magnitudes of the external forces.
Ceiling runner suspension devices which are designed for small scale medical facilities have comparatively low rigidity. In addition, radiation sources are provided at the lower ends of telescoping support columns that extend downward from ceiling horizontal movement bases. Therefore, there are cases in which the radiation sources sway like a pendulum at a specific oscillation frequency (unique oscillation frequency) corresponding to the supporting state of the ceiling runner suspension device. Further, there are cases in which the ceilings, on which the ceiling runner suspension devices are mounted, sway themselves. In these cases, the radiation sources sway by receiving the influence of the swaying ceilings as well.
The unique oscillation frequency, at which a radiation source oscillates, change according to the state of the ceiling on which a ceiling runner suspension device is provided, the rigidity of the ceiling runner suspension device, and the supporting state of the radiation source by the ceiling runner suspension device. The unique oscillation frequency varies according to the position of the ceiling runner suspension device along rails mounted on the ceiling (at the ends of the rails, and the center of the rails, etc.), the degree of expansion/contraction of a telescoping support column, and rotation (change of orientation) of the radiation source when changing from upright imaging to supine imaging, for example. Note that the oscillation frequency of the saying of the radiation source, which is supported by the ceiling runner suspension device, when the radiation source is caused to freely oscillate, is the unique oscillation frequency.
There are also cases in which that radiation source sways at the unique oscillation frequency when an operator urges an operating handle mounted thereon, to move the radiation source in the directions in which the urging force is applied at a speed corresponding to the magnitude of the external force, using the aforementioned power assistance function. In these cases, the urging force applied on the operating handle and the swaying of the radiation source at the unique oscillation frequency interfere with each other, and the force which is applied to the operating handle fluctuates periodically at the unique oscillation frequency.
If control of the power assistance function reacts to the fluctuations in the external force applied to the operating handle at the unique oscillation frequency, the swaying of the radiation source at the unique oscillation frequency is amplified, resulting in discomfort when operating the operating handle.
A possible measure that may be considered in order to suppress such swaying of the radiation source is to determine the frequency properties of the control of the power assistance function such that the control of the power assistance function does not react to the unique oscillation frequency of the sway of the radiation source (hereinafter, also referred to as “unique oscillation frequency of the oscillation of the radiation source”) at all positions that the radiation source is moved to. That is, the control of the power assistance function that moves the radiation source may be set such that it does not react to the unique oscillation frequency of the oscillation of the radiation source at all positions.
However, if this measure is adopted, the frequency properties of the control of the power assistance function are determined such that the power assistance function does not react to the unique oscillation frequencies of the oscillation of the radiation source. Therefore, the control of the power assistance reaction will become slow to react. That is, the movement of the radiation source according to manipulation of the operating handle will become delayed, and the operability of the operating handle will deteriorate.
Note that it is acceptable for the radiation source to move while freely oscillating at its unique oscillation frequency when an operator is manipulating the operating handle. However, if the free oscillation (oscillation at the unique oscillation frequency) of the radiation source is amplified under control of the power assistance function and the amplitude becomes greater, this is a problem, because the operability of the operating handle will deteriorate.
For this reason, there is demand to enable movement of radiation sources without delays in control of a power assistance function with respect to manipulation of operating handles, and also without oscillations at the unique oscillation frequencies of the radiation sources being amplified under control of a power assistance function.
Note that the aforementioned problem is related to radiation sources or radiation detectors, which are devices that are movably supported and are employed to perform radiation imaging. This problem commonly occurs when the devices are moved such that the movement tracks target values for movement (such as movement direction and movement speed), which are determined according to external forces applied to operating handles.